1. Field of the Invention
This invention relates to a novel optical information medium and the recording of information thereon. More particularly, the present invention relates to an optical information medium, the information layer of which comprises a naphthalocyanine chromophore. The present invention also relates to a synthesis of the naphthalocyanine chromophore.
2. Description of the Prior Art
Optical recording methods in which light from a laser is focused upon the surface of a recording medium with sufficient intensity to cause a detectable change in the physical characteristics of the surface material have been proposed. Among these methods is the establishment of an information pattern of pits. In such methods, the information representative pattern of pits may be formed in the surface of the recording medium by suitably controlling the intensity of the focused light in accordance with the information to be recorded while relative motion is established between the recording medium and the focused light spot.
For instance, in recent years, attention has been increasingly paid to the information recording method in which information is written in a thin film of metal or the like formed on a substrate by using a laser ray or beam. According to such a method, the information recording has been accomplished by forming holes or recesses in the metallic thin film under the action of a thermal energy beam such as a laser ray.
Organic materials have also been employed as the recording layer for optical data storage media, as described by Kuder in the Journal of Imaging Technology, Vol. 12, No. 3, pp. 140-143. These are typically thin films comprising either a dye in a polymer matrix, or a dye only. Organic recording layers are often more sensitive to the write laser beam than metal films due both to lower melting or softening temperatures and to low thermoconductivity. While metal films are typically sensitive to a broad spectrum of wavelengths, dyes used in organic media are narrow absorbers that must be carefully chosen so that the absorption matches the laser wavelength employed for writing. This disadvantage has led to a search for chromophores useful in optical data storage media which are sensitive specific to laser wavelengths.
The use of organic materials such as phthalocyanine and naphthalocyanine chromophores in optical recording media is known to the art. For example, the use of phthalocyanine dyes in conjunction with optical recording media comprising a styrene oligomer is disclosed in an article by Kuroiwa et al appearing in the Japanese Journal of Applied Physics, Vol. 22, No. 2, February 1983, pp. 340-343. Among the dyes and pigments discussed as being useful is a copper phthalocyanine pigment. The phthalocyanine dye conferred sensitivity to the helium-neon laser beam employed for data storage.
Japanese Patent Application No. 57-173,749, published April 9, 1984, of Kuroiwa et al, discloses an optical recording medium having alleged improved sensitivity. The recording medium comprises a recording layer composed of a polymer having a phthalocyanine residual group as a side chain.
There is described in U.S. Pat. No. 4,241,355 an ablative recording medium comprising a light reflecting layer and a light absorbing layer. This layer which absorbs light at from about 750 to 850 nanometers is comprised of a phthalocyanine pigment optionally substituted on the ring with chlorine, and with a central metal atom selected from the group consisting of lead, aluminum, vanadyl, or tin. Examples of specific pigments disclosed for use in the recording medium described include lead phthalocyanine, chloroaluminum-phthalocyanine, vanadyl phthalocyanine, stannic phthalocyanine, or chloro aluminum chloro phthalocyanine. According to the disclosure of the patent, these phthalocyanine compounds all absorb energy at solid state injection laser wavelengths and thus all can be evaporated onto a light reflecting layer to produce smooth, optical quality light absorption layers that form recorded information having high signal-to-noise ratios. The optical recording media disclosed in this patent were prepared by placing a reflective substrate in a vacuum chamber and causing, for example, a phthalocyanine such as lead phthalocyanine to be vacuum evaporated thereon.
There is described in U.S. Pat. No. 4,298,971 an optical recording medium wherein the recording layer consists entirely, or substantially entirely, of a compound of a metal oxide, or metal halide phthalocyanine, vacuum vapor deposited onto a substrate with or without a thin film of chalcogenide of tellurium. Examples of suitable phthalocyanines disclosed include vanadyl phthalocyanine, tin phthalocyanine, nickel phthalocyanine, aluminum phthalocyanine, zinc phthalocyanine, platinum phthalocyanine, and the like.
U.S. Pat. No. 4,529,688 discloses specific phthalocyanine compositions which are sensitive to infrared wavelengths and useful in ablative infrared optical recording devices. Such recording devices contain the infrared phthalocyanine photosensitive organic dyes dispersed in a polymeric resinous binder, and are useful with solid state injection lasers such as the Al-Ga-As laser system.
U.S. Pat. No. 4,458,004, issued July 3, 1984 to Tanikawa, discloses an optical information recording medium comprising a base and recording layer formed on the base. The recording layer comprises a fluorine phthalocyanine capable of absorbing light with a wavelength of 700 nm or more.
U.S. Pat. No. 4,492,750, issued January 8, 1985 to Law et al, discloses an ablative infrared-sensitive optical recording composition containing as a component thereof a dispersion of a resinous binder and a soluble naphthalocyanine.
U.S. Pat. No. 4,725,525 discloses the use of various substituted naphthalocyanine compounds in optical recording media, as does Japanese Kokai No. 177288, published August 8, 1986.
The recording medium, of course, is one of the key elements in any optical recording system, i.e., a system in which the information is recorded or read by light. Such a system would have a usefulness in the storage of audio and video information, data processing and document processing. The commercial viability of an optical recording medium would of course depend upon such technical parameters as the sharpness in recording and playback of the information, i.e., a high signal to noise ratio, as well as the useful life of the information medium. Maintaining the sensitivity of a recording medium throughout the cycles of record-read-erase is also an important consideration.
While dyes or pigments, including naphthalocyanine compounds, have been employed in information storage layers due to their excellent absorption properties, the search for an improved optical information storage medium exhibiting stability and intense absorption at specified wavelengths is continuously ongoing. The search for improved naphthalocyanine compounds for use in such optical storage media, which compounds exhibit improved properties with respect to solubility, etc., is also continuously ongoing. Such improved properties permit greater ease in the manufacture of the optical recording media, and hence can provide a more viable commercial product.
Accordingly, it is a major object of the present invention to provide a novel recording medium which comprises a naphthalocyanine chromophore.
Another object of the present invention is to provide a naphthalocyanine chromophore useful in optical recording media, which chromophore exhibits relatively improved solubility characteristics.
Yet another object of the present invention is to provide a novel process for the synthesis of such naphthalocyanine chromophores.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and the appended claims.